1. Field of the Invention
The present invention relates to a CMOS type solid-state imaging device and an imaging apparatus having such an element.
2. Description of the Related Art
Recently, imaging apparatus capable of imaging utilizing a solid-state imaging device and capable of storing resultant images have widely spread, such apparatus including digital still cameras and digital video cameras. CCD type solid-state imaging devices have been most commonly used as solid-state imaging devices of such imaging apparatus. However, there is a recent trend toward solid-state imaging devices having a greater number of pixels, as a result of which increasing attention is paid to CMOS type solid-state imaging devices.
A CMOS type solid-state imaging device is a solid-state imaging device which includes a pixel array section constituted by a two-dimensional array of a plurality of pixels each including a photoelectric conversion device and a plurality of pixel transistors or what are called MOS transistors and which read outs electrical signals obtained by converting electrical charges generated by the photoelectric conversion devices. CMOS type solid-state imaging devices are characterized by the capability of readout at a higher speed, higher sensitivity, and lower power consumption when compared to CCD type solid-state imaging devices. A CMOS type solid-state imaging device can be consolidated with analog circuits and logic circuits manufactured using CMOS processes into a single chip, and the resultant chip is therefore advantageous in that it requires a small number of peripheral ICs.
As shown in FIG. 16, a pixel array section 100 of a CMOS type solid-state imaging device has an optical black pixel region 102 provided outside an effective pixel region 101 which is illuminated by light. The region 102 includes pixels which are shielded from the illumination light to obtain an optical black level (hereinafter referred to as “optical black pixels”). The optical black pixels are configured to generate the same dark current as generated at effective pixels, and signals from the effective pixel region 101 are read out using the level of the dark current (black level) as a reference level. Thus, the magnitude of the dark current generated at the effective pixel region 101 is prevented from varying between the pixels therein, whereby the generation of noise having a fixed pattern and the generation of vertical stripes is suppressed. Fluctuations of signal levels at the effective pixel region 101 attributable to temperature changes can be also suppressed.
However, when intense light impinges on pixels of the effective pixel region 101 in the neighborhood of the optical black pixel region 102, the overflow of electrical charges occurs at the pixels of the effective pixel region 101, and electrical charges flow into the optical black pixel region 102 to increase the black level of the region 102, which phenomenon is called blooming. As a result, when outputs from the effective pixel region 101 are read out using the black level as a reference, a blackish dim image or an abnormal image will be generated. That is, an image of low quality will be reproduced.
One proposed solution to the problem is to provide a dummy pixel region in the form of an array of dummy pixels between an effective pixel region and an optical black pixel region (see JP-A-2006-222751 (Patent Document 1)).